function preloader(images) 
 {
 imageObj = new Image();
 for(i in images) 
  {
  imageObj.src=images[i];
  }
 } 

function on(el)
 {
 page_class = el.getAttribute("page")
 $(el.id+"_img").src="/im/"+page_class+"/on/"+el.id+".jpg"
 }

function off(el)
 {
 page_class = el.getAttribute("page")
 $(el.id+"_img").src="/im/"+page_class+"/"+el.id+".jpg"
 }